It is believed that dental plaque formed and adhered to the surface of teeth consists of 70% intraoral bacteria, approx. 20% polysaccharides synthesized by the bacteria and approx. 10% food debris. The intraoral bacterium Streptococcus mutans has been regarded as being cariogenic bacterium. Streptococcus mutans produces glucosyltransferase and dextran synthetase, these enzymes produce cohesive glucan which is principal component of dental plaque, for example, mutan, dextran or the like, from sucrose. In addition, acids produced and accumulated inside the dental plaque by this bacterium demineralize the enamel of teeth to induce dental caries. That is, the dental plaque is considered a causative of caries.